Nowadays, the gross of the global energy is decreasing day by day. Due to the rise of the oil price, the public are tending to go green with environment-friendly vehicles. The bicycle is one of the best choices, because it is green, environment-friendly and helps build the body. The foldable bicycle is very popular at present and there are various styles of foldable bicycles on sale.
For example, Chinese Patent Application No. CN200320131888.X, now Chinese Patent No. CN2656270, issued on Nov. 17, 2004, discloses a quickly foldable bicycle which can be longitudinally folded. As shown in FIG. 1 of the Chinese patent (which is not provided herein), the bicycle comprises a front arm 1, an intermediate arm 2 and a rear arm 3. The front arm 1 and the intermediate arm 2 are hinged together through a joint 12. The intermediate arm 2 and the rear arm 3 are hinged together through another joint 13. The lower end of the seat supporting pole 5 is connected with the connecting rod 7 and the connecting rod 8 respectively through a universal joint 9. The connecting rod 8 is connected with the rear arm 3 through a universal joint 11, and the connecting rod 7 is connected with the front arm 1 through a universal joint 10. The seat supporting pole 5 is slidably inserted inside the tube 4. The tube 4 is fixed on the intermediate arm 2. Thereby, a three-dimensional, intersectional and transformable pentagon is formed. An intermediate shaft is provided in front of the tube 4. As the two connecting rods both connect at two ends with the corresponding adjacent components through universal joints, the seat tube has the problem of swinging transversely from left to right, which makes the bicycle insecure and causes certain danger when a rider is riding the bicycle. What's more, the front end of the connecting rod 7 is provided at one side of the front arm 1, presenting a protruding component, which will give rise to insecure factors such as scraping, bumping and so on, and it is not very aesthetic either.
Chinese Patent Application No. CN201020515083.5, now Chinese Patent No. CN201784765, issued on Apr. 6, 2011, discloses a figure therein having a longitudinally foldable bicycle, wherein the front end of the front connecting rod 7 is also provided at one side of the front arm 1, presenting a protruding hinge shaft 10 at the connection. The protruding hinge shaft brings the risk of scraping or bumping the legs of the rider.